A liquid crystal display panel is widely used for portable information equipment because the liquid crystal display panel is light in weight, consumes less power, and is capable of performing display in a reflective type. Since contents to be displayed are diversified, a liquid crystal display panel of a matrix type is mainly used. In particular, development of an active matrix liquid crystal display panel, in which a switching element is formed for each pixel by reason of display quality, has been advanced.
For example, the active matrix liquid crystal display panel has plural gate electrodes arranged in an x direction, plural source electrodes arranged in a y direction, and plural thin-film transistors (TFTs) arranged at the nodes of the gate electrodes and the source electrodes on a first substrate. Display electrodes are connected to drain electrodes of thee thin-film transistors (TFTs). An opposed electrode is provided on a second substrate opposed to the first substrate on which the thin-film transistors (TFTs) are provided. Liquid crystal is encapsulated in a gap between the first substrate and the second substrate.
In the active matrix liquid crystal display panel formed in this way, an ON voltage is applied to the gate electrodes and data signal is applied to the source electrodes, whereby a predetermined voltage difference is provided between the display electrodes and the opposed electrode, and a predetermined voltage is applied to the liquid crystal to perform ON display.
Conversely, an OFF voltage is applied to the gate electrodes to bring the thin-film transistors (switching elements) into an OFF state, whereby a voltage difference does not occur between the display electrodes and the opposed electrode even if a data signal is applied to the source electrodes. This makes it possible to maintain the ON display or the OFF display. Therefore, moving image display can be performed by switching the ON and OFF signals to be applied to the gate electrodes and the data signal to be applied to the source electrodes in a temporal manner.
Moreover, combinations of pixels constituting a matrix make it possible to perform various kinds of representations. For example, the number of dots of 8×8 makes it possible to represent alphabets or numerals and the number of dots of 16×16 makes it possible to represent Chinese characters. However, with dot representation, for example it is difficult to represent a circle, a star, or a human shape with high accuracy, and problems occur in that, for example, the circle is represented as a polygon and an acute angle of the star cannot be reproduced. Therefore, when a complicated representation is performed with small pixels, a method of using a pictogram display area, in which display electrodes are constituted in an outer peripheral shape of a pictogram, is adopted.
As a liquid crystal display panel in which a moving image display area of an active matrix type and a pictogram display area of a static type are adopted for a display area, for example, there are techniques disclosed in Japanese Patent Application Laid-Open Publication No. 2001-183998 and Japanese Patent Application Laid-Open Publication No. 2001-117072.
In the active matrix liquid crystal display panel, damage to a switching element like a transistor and deterioration of liquid crystal tend to occur due to static electricity during a manufacturing process or during implementation of connection of the liquid crystal panel and an external circuit. As a result, display quality deteriorates. To prevent such deterioration of display quality due to static electricity, in the conventional active matrix liquid crystal display panel, a protective element is provided in each switching element as disclosed in, for example, Japanese Patent Application Laid-Open Publication No. H11-119256.
A display device described in Japanese Patent Application Laid-Open Publication No. 2001-183998 adopts a structure, which has thin-film transistors (TFTs) as switching elements, in a moving image display area and a structure of a static type, in which pictogram display electrodes are directly connected to wiring electrodes, is adopted in a pictogram display area. Japanese Patent Application Laid-Open Publication No. 2001-117072 discloses a technique in which an opposed electrode in a moving image display area and an opposed electrode in a pictogram display area are provided separately from each other and mutually supply optimal offset voltages. Japanese Patent Application Laid-Open Publication No. H11-119256 describes a structure in which protective elements are provided around a moving image display area.
As described above, in the conventional active matrix liquid crystal display panel, it is proposed that the pictogram display area should be provided together with the moving image display area and a measure against static electricity should be taken in the moving image display area. On the other hand, no measure is taken against static electricity that is generated in the pictogram display area. However, in actually forming the pictogram display area, electrodes for a pictogram and pictogram surrounding electrodes around a pictogram are provided according to circumstances. In this case, the electrode for a pictogram and the pictogram display surrounding electrode are adjacent to each other. Therefore, in the conventional liquid crystal display panel that does not take any measure against static electricity in the pictogram display area, there are problems in that deterioration of a gap around a pictogram due to static electricity, deterioration and seizing of liquid crystal due to static electricity, and the like occur, and high-quality display is not obtained.
As another problem, when a wiring electrode for applying a signal from the outside to the pictogram display electrodes is provided in the pictogram display area, this wiring electrode is seen from the outside to disturb display and, as a result, deteriorate display quality. When display is performed in the moving image display area and the pictogram display area simultaneously, it may become unclear which part is the moving image display area and which part is the pictogram display area, which leads to misrecognition of display.
For reduction in power consumption, display is not performed in the moving image display area but is performed only in the pictogram display area according to circumstances. However, in the conventional liquid crystal display panel, displayed contents may be mistaken because the pictogram display area is not clear. When display is performed only in the pictogram display area or a drive frequency is reduced for reduction in power consumption, if it is attempted to retain drive only with liquid crystal, display unevenness, seizing, and the like occur, and high-quality display is not obtained.
As described above, in the conventional liquid crystal display panel including the moving image display area and the pictogram display area, it is difficult to obtain a high display quality in both the display areas and perform high quality display particularly in the pictogram display area with low power consumption drive. The present invention has been devised in view of such points, and it is an object of the present invention to provide a new liquid crystal display panel in which a high display quality is obtained in both a moving image display area and a pictogram display area and display quality of the pictogram display area is never deteriorated even with low power consumption drive.